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[Lawrence London <lfljvenaura@gmail.com>]

Hardening chuck keys
http://www.practicalmachinist.com/vb/general/hardening-chuck-keys-260143/

1. Hardening chuck keys

   I made a couple of chuck keys today out of 1018 for the four jaw. I'm assuming I need to harden them. They won't be under much torque but will get a lot of use. What is recommended here? Is there enough carbon where I can quench it? Do I have to temper afterward? Should I get Kasenite? Or do I not need to harden them? The chuck key is .3" Thanks. Also, has anyone here heard of a chuck key being .3" Seemed odd to me...

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2. 02-07-2013, 08:45 PM #2

   Forrest Addy

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   Conventional wisdom is 1018 is the wrong material. A chuck key can be subject to high stresses and repeated use means wear. Then there is the handle which if made of low grade stuff will bend like a pretzel
   
   1018 deep carburized and heat treated to Rc 50-55 would work pretty well but a deeper hardening steel like oil or water hadening drill rod or some other high carbon steel would be better. There are proprietary case hardening (Kasenite, Hardn'Tough, etc) compounds that would enhance wear but have litttle penetration. In a chuck wrench you need deep strength because of the concentrated stresses. Consider where the square enters the chuck screw. A shallow case will fail because the underlying softer material yields and the square will ductile fail in tortion if not twist off.
   
   I strongly suggest you find most an hgh carbon or medium carbon alloy steel and start over; this time heat treating the wrench stem and the handle to spring temper.

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3. 02-07-2013, 08:55 PM #3

   sfriedberg

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   Oct 2010

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   If you are prone to ding or scar your keys, hardening would be beneficial. For plain wear resistance, hardening probably means replacement in 25 years instead of 5.
   
   1018 won't harden without help. Kasenite or Cherry Red (from Rose Mill) will do a nice job of case hardening without need for fancy equipment. Follow the instructions on the tin.
   
   At one point I had three chucks, none of which took sensible key sizes (either Imperial or metric). Bought the next size up stock keys and ground down the squares to fit. Seems like chuck key sizes aren't the least bit standardized.